Transmission breather system

ABSTRACT

A transmission breather system is provided in which a subassembly is formed by supporting a shift select shaft, moving in the axial direction according to a select operation of a shift lever, and a select spring, maintaining the shift select shaft in a neutral position, on a cover member. Moreover, a breather chamber is formed between the cover member and an indentation of a transmission case by inserting the shift select shaft into an opening formed on the bottom wall of the indentation of the transmission case to connect the cover member to the transmission case, and the select spring is housed in the breather chamber. Thus, with regard to the transmission breather system, it is possible to form a breather chamber whose maintenance is easy while avoiding an increase in the size of the transmission case.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a breather system for a transmission inwhich a plurality of gear shift stages are selectively established bymoving shift forks by means of a shift select shaft, moving in an axialdirection according to a select operation of a shift lever and moving ina circular manner according to the shift operation thereof.

2. Description of the Prior Art

A transmission containing a breather chamber is known in U.S. Pat. No.4,446,755. This breather chamber is formed from a rib which is connectedto the inner wall surface of a transmission case and a rib which isconnected to the inner wall surface of a clutch case, to bridge theconnecting surface between the two cases, and the breather chamber isconnected through to the internal space of the transmission case via anotch formed in the rib.

However, since a special breather chamber is formed on the connectingsurface between the transmission case and the clutch case in the priorart, not only does the overall size of the transmission increase due tothe volume of the breather chamber, but also maintenance of the breatherchamber cannot be carried out without separating the transmission casefrom the clutch case, which is an extremely troublesome operation.

SUMMARY OF THE INVENTION

The present invention has been carried out in view of theabove-mentioned circumstances, and it is an objective of the presentinvention to form a breather chamber whose maintenance is easy whileavoiding an increase in the size of the transmission case.

In order to achieve the above-mentioned objective, in accordance withthe present invention a transmission breather system is provided whichis a breather system for a transmission in which a plurality of gearshift stages are selectively established by moving shift forks by meansof a shift select shaft, moving in the axial direction according to aselect operation of a shift lever and moving in a circular manneraccording to a shift operation thereof. A subassembly is formed bysupporting the shift select shaft and a select spring, which maintainsthe shift select shaft in a neutral position, on a cover member. Abreather chamber is formed between the cover member and an indentationformed in a transmission case by inserting the shift select shaft intoan opening formed on the bottom wall of the indentation of thetransmission case so as to connect the cover member to the transmissioncase, and the select spring is housed in the breather chamber.

In accordance with the above-mentioned arrangement, since thesubassembly is made by supporting the shift select shaft and the selectspring on the cover member and the shift select shaft of the subassemblyis inserted into the opening formed on the bottom wall of theindentation of the transmission case to connect the cover member to thetransmission case, not only does the operation of assembling the shiftselect shaft and the select spring become easy, but also the spacerequired for housing the select spring can be used as the breatherchamber, contributing to a reduction in the size of the transmissioncase. Moreover, maintenance can be carried out by simply removing thesubassembly from the transmission case to expose the internal space ofthe breather chamber.

Furthermore, in accordance with the:present invention, a breather systemfor a transmission is proposed wherein a spring seat for supporting oneend of the select spring is supported on the bottom wall of theindentation, and the breather chamber is connected through to theinternal space of the transmission case via a through hole which isformed between the outer circumference of the spring seat and the innercircumference of the opening.

In accordance with the above-mentioned arrangement, since the breatherchamber is connected through to the internal space of the transmissioncase via the through hole between the outer circumference of the springseat for supporting one end of the select spring and the innercircumference of the opening of the transmission case, it is possible toprevent oil inside the transmission case from entering the breatherchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a manual transmission for avehicle.

FIG. 2 is a diagram showing the change patterns of a change lever.

FIG. 3 is a horizontal cross-sectional view of an essential part of themanual transmission for a vehicle.

FIG. 4 is a magnified view of an essential part of FIG. 3 (thirdspeed-fourth speed select position).

FIG. 5 is a cross-sectional view at line 5—5 in FIG. 4.

FIG. 6 is a view for explaining an action corresponding to FIG. 4 (fifthspeed-reverse select position).

FIG. 7 is a view for explaining an action corresponding to FIG. 4 (firstspeed-second speed select position).

FIG. 8 is a view taken in the direction of an arrow 8 in FIG. 3.

FIG. 9 is a cross-sectional view at line 9—9 in FIG. 8.

FIG. 10 is a magnified view of an essential part of FIG. 8 (neutralposition).

FIG. 11 is a view for explaining an action corresponding to FIG. 10(reverse position).

FIG. 12 is a view for explaining an action corresponding to FIG. 10(fifth speed position).

FIG. 13 is a view from line 13—13 in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 a transmission case 11 for a manual transmission Mfor vehicle with five forward speeds and one reverse speed, comprises acase left half 12 and a case right half 13 which are separated on adividing plane extending in the longitudinal direction of the vehicle,and a gear shift clutch C is housed in a clutch chamber 14 formed on theside surface of the case left half 12 on the side of the engine E. Theright and left ends of a main shaft Sm connected to the engine E via thegear shift clutch C, are supported by means of ball bearings 16 and 15on the case right half 13 and the case left half 12 respectively, andthe right and left ends of a counter shaft Sc positioned in parallel tothe main shaft Sm are supported by ball bearings 18 and roller bearings17 on the case right half 13 and the case left half 12 respectively. Adifferential gear D which distributes the output from the counter shaftSc to the right and left axles 19, 19 is supported by a pair of rightand left ball bearings 21, 20 on the case right half 13 and the caseleft half 12 respectively.

The gear shift clutch C housed inside the clutch chamber 14, comprises aclutch wheel 22 which is connected to the right end of the crankshaft ofthe engine E and a clutch disc 24, connected to the left end of the mainshaft Sm via a damper 23. They are normally engaged by clamping thefacings 27 of the clutch disc 24 between a pressure plate 26 and theclutch wheel 22 by means of the resilient force of a diaphragm spring 25and the engagement is released during gear shifting by means of arelease fork 28 pushing a release bearing 29 leftwards.

On the main shaft Sm are secured a main first speed gear 31, a mainsecond speed gear 32, a main third speed gear 33, a main fourth speedgear 34 and a main fifth speed gear 35, which are all supported in arelatively rotatable manner. On the counter shaft Sc, a counter firstspeed gear 36 and a counter second speed gear 37 which mesh with themain first speed gear 31 and main second speed gear 32, are supported ina relatively rotatable manner. A counter third speed gear 38, a counterfourth speed gear 39 and a counter fifth speed gear 40 are also securedwith counter shaft Sc and mesh with the main third speed gear 33, mainfourth speed gear 34 and main fifth speed gear 35 respectively.

The right and left ends of a reverse idle shaft Sr are supported on thecase right half 13 and the case left half 12, and a reverse idle gear 41which is supported on the reverse idle shaft Sr, in a laterally slidablemanner, can mesh with a main reverse gear 42 which is secured on themain shaft Sm as well as with a counter reverse gear 43 which issupported on the counter shaft Sc in a relatively rotatable manner.

By moving a sleeve 45 of a first speed-second speed synchronousmechanism S1 leftwards by means of a first speed-second speed shift fork44, the counter first speed gear 36 is connected to the counter shaft Scto establish a first speed gear shift stage, and by moving the sleeve 45of the first speed-second speed synchronous mechanism S1 rightwards bymeans of the first speed-second speed shift fork 44, the counter secondspeed gear 37 is connected to the counter shaft Sc to establish a secondspeed gear shift stage. By moving a sleeve 47 of a third speed-fourthspeed synchronous mechanism S2 leftwards by means of a thirdspeed-fourth speed shift fork 46 the main third speed gear 33 isconnected to the main shaft Sm to establish a third speed gear shiftstage, and by moving the sleeve 47 of the third speed-fourth speedsynchronous mechanism S2 rightwards by means of the third speed-fourthspeed shift fork 46, the main fourth speed gear 34 is connected to themain shaft Sm to establish a fourth speed gear shift stage.

By moving a sleeve 49 of a fifth speed synchronous mechanism S3leftwards by means of a fifth speed shift fork 48, the main fifth speedgear 35 is connected to the main shaft Sm to establish a fifth speedgear shift stage. When the sleeve 49 of the fifth speed synchronousmechanism S3 is moved rightwards by means of the fifth speed shift fork48, a reverse shift fork 50 which supports the reverse idle gear 41 in arotatable manner, moves leftwards in operative connection with the fifthspeed shift fork 48, and the reverse idle gear 41 meshes with the mainreverse gear 42 and the counter reverse gear 43 provided on the sleeve45 of the first speed-second speed synchronous mechanism S1, toestablish a reverse gear shift stage.

The first speed-second speed synchronous mechanism S1, the thirdspeed-fourth speed synchronous mechanism S2 and the fifth speedsynchronous mechanism S3 are known and they carry out a synchronousaction by means of the frictional force between a blocking ring and asynchro cone due to the lateral movement of the sleeves 45, 47 and 49.

When the first to fifth gear shift stage or reverse gear shift stage isthus established, rotation of the counter shaft Sc is transmitted to thedifferential gear D via a final drive gear 51 and a final driven gear 52thus driving the right and left axles 19, 19.

The structure of a shifting system for establishing the first speed tofifth speed gear shift stages and the reverse gear shift stage isexplained below by reference to FIG. 2 to FIG. 12.

FIG. 2 shows an operational pattern of a shift lever L of the shiftingsystem; P1 denotes a first speed-second speed select position, P2denotes a third speed-fourth speed select position (neutral position),P3 denotes a fifth speed-reverse select position, {circle around (1)}and {circle around (2)} which are located on either side of the firstspeed-second speed select position P1, denote a first speed position anda second speed position respectively, {circle around (3)} and {circlearound (4)} which are located on either side of the third speed-fourthspeed select position P2, denote a third speed position and a fourthspeed position respectively, and {circle around (5)} and R which arelocated on either side of the fifth speed-reverse select position P3,denote a fifth speed position and a reverse position respectively. Thearrow SE in the figure illustrates the directions of the selectoperation of the shift lever L and the arrow SI in the figureillustrates the directions of the shift operation of the shift lever L.

As shown in FIG. 3 to FIG. 5, a dish-shaped indentation 13 a is formedon the upper part of the case right half 13 of the transmission case 11,and by connecting a cover member 57 by means of six bolts 56 to coverthe opening of the indentation 13 a, a breather chamber 58 is formedbetween the cover member 57 and the indentation 13 a. A shift selectshaft 59 is supported in a rotatably and longitudinally movable mannerin a guide hole 57 a formed in the center of the cover member 57 and aguide hole 13 b formed inside the case right half 13.

A notch 59 a is formed on the upper end of the shift select shaft 59which extends externally from the cover member 57 via a sealing member60, and a select lever 61 engages with the notch 59 a. The select lever61 swings vertically in operative connection with the select operation(operation in the direction of the arrow SE in FIG. 2) of the shiftlever L and can move the shift select shaft 59 between the thirdspeed-fourth speed select position shown in FIG. 4, the fifthspeed-reverse select position (see FIG. 6), which is upwards relative tothe third speed-fourth speed select position, and the first speed secondspeed select position (FIG. 7), which is downwards relative to the thirdspeed-fourth speed select position.

A shift lever 62 is fixed beneath the notch 59 a of the shift selectshaft 59, and the shift lever 62 rotates in lateral directions inoperative connection with the shift operation (operation in thedirection of the arrow SI in FIG. 2) of the shift lever L. When theshift lever L is in the first speed-second speed select position P1, thethird speed-fourth speed select position P2 or the fifth speed-reverseselect position P3, the shift select shaft 59 is in the neutralposition; when the shift lever L is operated to move to the first speedposition {circle around (1)}, the third speed position {circle around(3)} or the fifth speed position {circle around (5)}, the shift selectshaft 59 rotates leftwards from the neutral position, and when the shiftlever L is operated to move to the second speed position {circle around(2)}, the fourth speed position {circle around (4)} or the reverseposition R, the shift select shaft 59 rotates rightwards from theneutral position. The shift select shaft 59 can be stopped at nodalpoints in the three rotational positions by means of a detent mechanism63 (FIG. 8).

A shift arm 64 is fixed by a fixing pin 65 on the shift select shaft 59which extends inside the case right half 13, and an interlock plate 66is also supported on the shaft 59 in a relatively rotatable manner suchthat the shift arm 64 is vertically sandwiched by the plate 64. Theinterlock plate 66 comprises a pair of upper and lower lock claws 66 a,66 b, and the pair of lock claws 66 a, 66 b face the top and bottomrespectively of a drive part 64 a formed at the forward end of the shiftarm 64. The interlock plate 66 comprises a guide channel 66 c whichextends in a direction perpendicular to the shift select shaft 59 and arotation stopping pin 67 fixed on the case right half 13 engages withthe guide channel 66 c.

Therefore, when the shift select shaft 59 moves vertically, the shiftarm 64 and the interlock plate 66 ascend and descend together, but whenthe shift select shaft 59 rotates, the shift arm 64 rotates togetherwith the shift select shaft 59, but rotation of the interlock plate 66is restricted by engagement of the guide channel 66 c with the rotationstopping pin 67.

The shift select shaft 59 has a lower half with a smaller diameterbeneath a step-shaped first stopper surface 59 b which is formed almostat its center in the longitudinal direction, and the upper surface ofthe inner circumference of a first spring seat 68 which fits in aslidable manner on the lower half of the shift select shaft 59 havingthe smaller diameter, engages with the first stopper surface 59 b fromthe lower side, whereas the upper surface of the outer circumference ofthe first spring seat 68 is in contact with a first support surface 57 bwhich is a lower surface of the cover member 57. With regard to adisc-shaped second spring seat 69 which is placed beneath thefirst-spring seat 68 and fits in a slidable manner on the shift selectshaft 59, the lower surface of the inner circumference thereof engageswith a second stopper surface 66 d which is formed on the upper surfaceof the interlock plate 66. A roughly cross-shaped opening 13 c is formedon the bottom wall of the indentation 13 a of the case right half 13,and the lower surface of the outer circumference of the second springseat 69 is supported by four step-shaped second supporting surfaces 13 dwhich are formed on the edge of the opening 13 c. The upper and lowerends of a select spring 70 are supported between the lower surface ofthe first spring seat 68 and the upper surface of the second spring seat69.

Thus, when the shift select shaft 59 is in the three speed-fourth speedselect position shown in FIG. 4, the upper surface of the innercircumference of the first spring seat 68 and the lower surface of theinner circumference of the second spring seat 69 which are supported ina slidable manner on the shift select shaft 59 and are forced by theselect spring 70 in a direction such that they move apart from eachother, are resiliently in contact with both the first stopper surface 59b of the shift select shaft 59 and with the second stopper surface 66 dformed on the upper surface of the interlock plate 66, and the uppersurface of the outer circumference of the first spring seat 68 and thelower surface of the outer circumference of the second spring seat 69are supported by being in contact with the first support surface 57 b ofthe cover member 57 and with the second support surfaces 13 d of theindentation 13 a respectively, and the shift select shaft 59 thus stopsin a stable manner at the third speed-fourth speed select position.

When the shift select shaft 59 moves upwards from the above-mentionedstate to the fifth speed-reverse select position (FIG. 6), since thesecond spring seat 69 which is pressed by the second stopper surface 66d of the interlock plate 66 which is integral with the shift selectshaft 59, ascends while leaving the first spring seat 68 which islatched onto the first support surface 57 b of the cover member 57 atits original position, the select spring 70 is compressed, generating aforce to return the shift select shaft 59 to the third speed-fourthspeed select position.

On the other hand, when the shift select shaft 59 moves downwards fromthe third speed-fourth speed position to the first speed-second speedselect position (FIG. 7), since the first spring seat 68 which ispressed by the first stopper surface 59 b of the shift select shaft 59,descends while leaving the second spring seat 69 which is latched ontothe second support surfaces 13 d of the opening 13 c, at its originalposition, the select spring 70 is compressed, generating a force toreturn the shift select shaft 59 to the third speed-fourth speed selectposition.

As hereinbefore described, since the shift select shaft 59 can becentered by forcing it to the third speed-fourth speed select position,which is the neutral position, by means of just one select spring 70, incomparison with the case in which the shift select shaft 59 is forcedupwards and downwards by means of two springs, the number of parts andthe cost can be reduced. Moreover, when two springs are supported on theshift select shaft 59, the length of the shift select shaft 59inevitably increases, but by using only one spring it is possible toreduce the overall length of the shift select shaft 59.

The internal space of the breather chamber 58 which is defined by theindentation 13 a of the case right half 13 and the cover member 57 isconnected to the internal space of the transmission case 11 via fourthrough holes 71 which are formed between the inner circumference of theopening 13 c and the outer circumference of the second spring seat 69and is connected to the outside of the transmission case 11 via abreather tube 73 provided on the forward end of a breather pipe 72,which is integral with the cover member 57.

A subassembly A is formed by assembling the shift select shaft 59, thefirst spring seat 68, the second spring seat 69, the select spring 70,the shift arm 64, the fixing pin 65 and the interlock plate 66beforehand, onto the cover member 57, and by inserting this subassembly.A into the opening 13 c through the indentation 13 a of the case righthalf 13 during assembly. Thus, the assembly operation can beoutstandingly enhanced.

Since the breather chamber 58 is defined by the indentation 13 a of thecase right half 13 and the cover member 57, and the first spring seat68, the second spring seat 69 and the select spring 70 are housed insidethe breather chamber 58, a single space functions as both the spaceforming the breather chamber 58 and the space for housing the firstspring seat 68, the second spring seat 69 and the select spring 70, andit is possible to avoid an increase in the size of the transmission case11 and the number of parts. Moreover, since the breather chamber 58 isconnected to the internal space of the transmission case 11 via the fourthrough holes 71 which are formed between the inner circumference of theopening 13 c and the outer circumference of the second spring seat 69,and the shift arm 64 and the interlock plate 66 are positioned so as toadjoin each other beneath the through holes 71, oil can be effectivelyprevented from entering the breather chamber 58 due to the labyrintheffect.

As shown in FIG. 4 and FIG. 8, the two ends of a first speed-secondspeed shift rod 76 comprising the first speed-second speed shift fork44, the two ends of a third speed-fourth speed shift rod 77 comprisingthe third speed-fourth speed shift fork 46 and the two ends of a fifthspeed-reverse shift rod 78 comprising the fifth speed shift fork 48 aresupported in a slidable manner on the case left half 12 and the caseright half 13 respectively. A first speed-second speed shift piece 79, athird speed-fourth speed shift piece 80 and a fifth speed-reverse shiftpiece 81 are fixed on the first speed-second speed shift rod 76, thethird speed-fourth speed shift rod 77 and the fifth speed-reverse shiftrod 78 respectively, and notches 79 a, 80 a, 81 a formed at the forwardends of the three shift pieces 79, 80, 81 respectively are alignedvertically so that they can selectively engage with the drive part 64 aprovided at the forward end of the shift arm 64.

Thus, when the shift select shaft 59 is in the third speed-fourth speedselect position as shown in FIG. 4, since the drive part 64 a of theshift arm 64 engages with the notch 80 a of the third speed-fourth speedshift piece 80, the third speed-fourth speed shift rod 77 can be driventogether with the third speed-fourth speed shift piece 80 from theneutral position to the third speed position or the fourth speedposition by a circular movement of the shift select shaft 59. At thisstage, the locking claw 66 b on the lower side of the interlock plate 66engages with the notch 79 a of the first speed-second speed shift piece79, and the locking claw 66 a on the upper side of the interlock plate66 engages with the notch 81 a of the fifth speed-reverse shift piece81, and thus malfunctions of the first speed-second speed shift piece 79and the fifth speed-reverse shift piece 81 can be prevented.

As shown in FIG. 7, when the shift select shaft 59 is moved to the firstspeed-second speed select position which is beneath the thirdspeed-fourth speed select position, since the drive part 64 a of theshift arm 64 engages with the notch 79 a of the first speed-second speedshift piece 79, the first speed-second speed shift rod 76 can be driventogether with the first speed-second speed piece 79 from the neutralposition to the first speed position or the second speed position by acircular movement of the shift select shaft 59. At this stage, thelocking claw 66 a on the upper side of the interlock plate 66 engageswith the notch 81 a of the fifth speed-reverse shift piece 81 and thenotch 80 a of the third speed-fourth speed shift piece 80, and thusmalfunctions of the fifth speed-reverse shift piece 81 and the thirdspeed-fourth speed shift piece 80 can be prevented.

As shown in FIG. 6, when the shift select shaft 59 is moved to the fifthspeed-reverse select position which is above the third speed-fourthspeed select position, since the drive part 64 a of the shift arm 64engages with the notch 81 a of the fifth speed-reverse shift piece 81,the fifth speed-reverse shift rod 78 can be driven together with thefifth speed-reverse shift piece 81 from the neutral position to thefifth speed position or the reverse position by a circular movement ofthe shift select shaft 59. At this stage, the locking claw 66 b on thelower side of the interlock plate 66 engages with the notch 79 a of thefirst speed-second speed shift piece 79 and the notch 80 a of the thirdspeed-fourth speed shift piece 80, and thus malfunctions of the firstspeed-second speed shift piece 79 and the third speed-fourth speed shiftpiece 80 can be prevented.

As shown in FIG. 8, a detent mechanism 82 is provided in order to stopthe first speed-second speed shift rod 76 at nodal points so as tocorrespond to the first speed-second speed select position, the firstspeed position and the second speed position. Moreover, a detentmechanism 83 is provided in order to stop the third speed-fourth speedshift rod 77 at nodal points so as to correspond to the thirdspeed-fourth speed select position, the third speed position and thefourth speed position.

As shown in FIG. 8 to FIG. 10, a bracket 85 is fixed to the innersurface of the case right half 13 by means of two bolts 86, 86, and thereverse shift fork 50 is supported in a swingable manner on the bracket85 via a fulcrum pin 87. A notch 50 a which is interposed between thetwo side surfaces of the reverse idle gear 41 is formed at one end ofthe reverse shift fork 50 and a driven cam face a for reverse shift, adriven cam face b for neutral return and a driven cam face c for neutralhold are formed continuously at the other end, relative to the fulcrumpin 87, of the reverse shift fork 50. A drive cam face d for reverseshift which can come into contact with the driven cam face c for reverseshift and a drive cam face e for neutral return which can come intocontact with the driven cam face b for neutral return and the driven camface c for neutral hold, are formed continuously at the forward end ofthe drive cam 88, which is formed integrally with the fifthspeed-reverse shift piece 81.

A detent mechanism 84 for stopping the fifth speed-reverse shift rod 78at nodal points to correspond to the fifth speed-reverse selectposition, the fifth speed position and the reverse position is providedat the forward end of an arm 85 a which extends integrally from thebracket 85 supporting the reverse shift fork 50. As shown in FIG. 9, thedetent mechanism 84 comprises a detent ball 84 b which is urged by adetent spring 84 a, and this detent ball 84 b can selectively engagewith three indentations 81 b to 81 d (FIG. 10 to FIG. 12) which areformed on the fifth speed-reverse shift piece 81.

Thus, when the fifth speed-reverse shift piece 81 is at the neutralposition as shown in FIG. 10, the drive cam face d for reverse shift andthe drive cam face c for neutral return of the drive cam 88 of the fifthspeed-reverse shift piece 81 are in contact with the driven cam face afor reverse shift and the driven cam face c for neutral hold of thereverse shift fork 50 respectively, and the reverse idle gear 41 is atthe neutral position which is at the right end on the reverse idle shaftSr and is in contact with the end face 13 i of the case right half 13.Therefore, even if the reverse idle gear 41 attempts to move leftwardsso as to move away from the end face 13 i of the case right half 13, theleftward movement of the reverse idle gear 41 is prevented by thecontact between the drive cam face e for neutral return of the drive cam88 and the driven cam face c for neutral hold of the reverse shift fork50.

As shown in FIG. 12, when the fifth speed-reverse shift rod 78 movesleftwards from the neutral position to the fifth speed position in orderto establish a fifth speed gear shift stage, the main fifth speed gear35 is linked to the main shaft Sm by the fifth speed shift fork 48,which is provided on the fifth speed-reverse shift rod 78, to establishthe fifth speed gear shift stage (FIG. 1). At this stage, the drive camface e for neutral return of the drive cam 88 which operates integrallywith the fifth speed-reverse shift rod 78 moves to slide along thedriven cam face c for neutral hold of the reverse shift fork 50, and thereverse shift fork 50 remains stopped at the neutral position. In thiscase also, even if the reverse idle gear 41 attempts to move leftwardsso as to move away from the end face 13 i of the case right half 13, theleftward movement of the reverse idle gear 41 is prevented by thecontact between the drive cam face e for neutral return of the drive cam88 and the driven cam face c for neutral hold of the reverse shift fork50.

When the fifth speed-reverse shift rod 78 moves rightwards from thefifth position (FIG. 11) to the neutral position (FIG. 10) in order torelease an established fifth gear shift stage, since the drive cam facee for neutral return of the drive cam 88 moves to slide along the drivencam face c for neutral hold of the reverse shift fork 50, the reverseshift fork 50 remains stopped at the neutral position.

As shown in FIG. 11, when the fifth speed-reverse shift rod 78 movesrightwards from the neutral position to the reverse position in order toestablish a reverse gear shift stage, the fifth speed shift fork 48provided on the fifth speed-reverse shift rod 78 slips rightwards (FIG.1). At the same time, the drive cam face d for reverse shift of thedrive cam 88 which operates integrally with the fifth speed-reverseshift rod 78 presses against the driven cam face a for reverse shift ofthe reverse shift fork 50, swinging the reverse shift fork 50anticlockwise. As a result, the reverse shift fork 50 slides the reverseidle gear 41 leftwards along the reverse idle shaft Sr, and the reverseidle gear 41 meshes with the main reverse gear 42 and the counterreverse gear 43 to establish a reverse gear shift stage.

In this state, the left end face of the reverse idle gear 41 is incontact with the end face 12 b of the case left half 12, and even if thereverse idle gear 41 attempts to move rightwards therefrom, therightward movement of the reverse idle gear 41 is prevented by thecontact between the drive cam face d for reverse shift of the drive cam88 and the driven cam face a for reverse shift of the reverse shift fork50.

When the fifth speed-reverse shift rod 78 moves leftwards from thereverse position (FIG. 12) to the neutral position (FIG. 10) in order torelease an established reverse gear shift stage, the drive cam face efor neutral return of the drive cam 88 presses against the driven camface b for neutral return of the reverse shift fork 50, swinging thereverse shift fork 50 clockwise. As a result, the reverse shift fork 50slides the reverse idle gear 41 rightwards along the reverse idle shaftSr, and the reverse idle gear 41 moves away from the main reverse gear42 and the counter reverse gear 43 to release the established reversegear shift stage.

As is clear from FIG. 10 and FIG. 13, with regard to the reverse idleshaft Sr, its left end is held by being fitted in a shaft support hole12 a which is formed in the case left half 12 and its right end is heldby being fitted in a shaft support hole 13 e which is formed in the caseright half 13. The inner wall surface of the shaft support hole 13 e ofthe case right half 13 is not closed in the circumferential direction,and a portion thereof opens in the direction facing the main shaft Smvia a notch. That is to say, a shaft support surface 13 f of the shaftsupport hole 13 e which supports the reverse idle shaft Sr comprises amajor arc having an angle of about 250°, and a portion of the outercircumference of the reverse idle shaft Sr is exposed to the internalspace of the case right half 13 through an opening 13 g comprising aminor arc having an angle of about 110°. Thus, even when a portion ofthe inner wall surface of the shaft support hole 13 e is lacking, if theshaft support surface 13 f of the shaft support hole 13 e has a centralangle of 180° or more, there is no possibility of the reverse idle shaftSr dropping from the shaft support hole 13 e.

As shown by the broken line in FIG. 8, if the shaft support hole 13 e ismade in the form of a closed pocket, since an inner wall surface 13 h ofthe case right half 13 projects into the inside of the transmission case11, there is a possibility of the inner wall surface 13 h interferingwith a gear provided on the main shaft Sm, and if the distance betweenthe reverse idle shaft Sr and the main shaft Sm is increased in order toavoid the interference, there is the problem that the size of thetransmission case 11 increases. However, by cutting a portion of theshaft support hole 13 e for the reverse idle shaft Sr as in the presentembodiment, the size of the transmission case 11 can be reduced byallowing the reverse idle shaft Sr to approach the main shaft Sm asclosely as possible without providing a special member for supportingthe reverse idle shaft Sr or carrying out special processing.

Although a manual transmission M is illustrated in the embodiment, thepresent invention can be applied to an automatic transmission in whichthe shift/select operation is carried out by an actuator.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresently disclosed embodiment is therefore to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, rather than the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are, therefore, to be embraced therein.

What is claimed is:
 1. A breather system for a transmission including atransmission case, a plurality of shift forks, a shift select shaft, ashift lever, and a select spring, for selectively establishing aplurality of gear shift stages wherein the shift forks are operated bythe shift select shaft supported on the transmission case, the shiftselect shaft being moved in the axial direction according to a selectoperation of the shift lever and being moved in a circular manneraccording to a shift operation of the shift lever, the breather systemhaving a subassembly comprising the shift select shaft, the selectspring for biasing the shift select shaft towards a neutral position,and a cover member coupled to the transmission case such that a breatherchamber is formed between the cover member and an indentation formed inthe transmission case, wherein the shift select shaft passes through anopening formed in the bottom wall of the indentation and wherein theselect spring is housed in the breather chamber.
 2. A breather systemfor a transmission according to claim 1, wherein a spring seat forsupporting one end of the select spring is supported on the bottom wallof the indentation, and the breather chamber is connected through to theinternal space of the transmission case by a through hole formed betweenthe outer circumference of the spring seat and the inner circumferenceof the opening.